The U.S. Army Corps of Engineers has uncovered what could be a fourth major disposal area for World War I-era munitions and chemical weapons in the nation’s capital.

Digging was suspended April 8 as a precaution at the site in the pricey Spring Valley neighborhood near American University after workers pulled smoking glassware from the pit, project manager Dan Noble said Thursday.

Preliminary tests show the glassware was contaminated with the toxic chemical arsenic trichloride. Officials will review safety procedures before digging continues.

Workers also discovered a jar about three-quarters full of a dark liquid that turned out to be the chemical agent mustard. It was used during World War I as a weapon that caused blisters, breathing problems and vomiting.

“It’s a much larger disposal area than we predicted,” Noble said. “The nature of debris is so different, perhaps it’s a different disposal area.”

It’s too soon to know for sure, Noble said.

During World War I, the Army used the university as an experiment station to develop and test chemical weapons. Previously, there were three known sites where weapons and chemicals were buried.

Glassware, chemicals, contaminated soil and munitions have been found since January in the front yard of a home next door to the university president’s house, the Army Corps has revealed. About 30 intact items were sent to an Army lab in Edgewood, Md., for testing, Noble said.

American University spokeswoman Camille Lepre said there were no plans to move or cancel any campus events scheduled at the president’s house.

About 350 pounds of glassware and debris had been removed from the site, along with about 676 barrels of soil, according to a campus memo Wednesday by university president Neil Kerwin.